Internet Engineering Task Force (IETF) K. Fujiwara
Request for Comments: 5825 JPRS
Category: Experimental B. Leiba
ISSN: 2070-1721 Huawei Technologies
April 2010
Displaying Downgraded Messages for Email Address Internationalization
Abstract
This document describes a method for displaying downgraded messages
that originally contained internationalized email addresses or
internationalized header fields.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.
This document defines an Experimental Protocol for the Internet
community. This document is a product of the Internet Engineering
Task Force (IETF). It represents the consensus of the IETF
community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents approved by the IESG are a candidate for any level of
Internet Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5825.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Fujiwara & Leiba Experimental [Page 1]RFC 5825 Displaying Downgraded Messages April 2010Table of Contents
1. Introduction ....................................................2
2. Terminology .....................................................2
3. Converting Downgraded Message Headers for Display ...............3
3.1. Considerations .............................................3
3.2. The Process ................................................3
3.2.1. No Reconstruction of the Envelope
Information Preservation ............................4
3.2.2. Reconstructing the Address Header Fields'
Preservation Header .................................4
3.2.3. The Unknown Header Fields' Preservation
Header Fields .......................................5
4. Security Considerations .........................................6
5. Acknowledgements ................................................6
6. References ......................................................6
6.1. Normative References .......................................6
6.2. Informative References .....................................7
Appendix A. Examples ..............................................8
A.1. Displaying Example ........................................11
1. Introduction
The Email Address Internationalization (UTF8SMTP) extension document
set [RFC4952] [RFC5336] [RFC5335] [RFC5337] expands Email address
structure, syntax, and email header format. To avoid rejection of
internationalized email messages, the downgrading mechanism [RFC5504]
converts an internationalized message to a traditional email message
when a server in the delivery path does not support the UTF8SMTP
extension. The downgraded message is a traditional email message,
except the message has "Downgraded-" header fields.
A perfect reverse-function of the downgrading does not exist because
the encoding defined in [RFC2047] is not exactly reversible and
"Received" header field downgrading may remove FOR clause
information. The restoration of the downgrading should be done once
at the final destination of the downgraded message such as Mail User
Agents (MUAs) or IMAP servers. This document describes the
restoration methods for displaying downgraded messages in MUAs.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this